Wave guide



- H. c. EARLY 2,479,220

WAVEGUIDE Aug. 16, 1949.

Filed Aug. 1, 1945 I I M I g, I I '4 l6 20 I2 I8 l9 I II.

FIG. I

F I G. 3

INVENTOR,

HAROLD C. EARLY ATTORNEY.

Patented Aug. 16, 1949 v Harold" C.' Eai'ly', Canihridge,Mass.,-assignor .to theUIiite'dLStateSof Americaas represented by a "the Secr'etaryofWar sApplicationAugust -1, 1945,Serial2N0. 608,319

This invention f relates generally .to .the transmission ofradiojfrequency energy; Mordparticularly, .it.-r elates Lto waveguidesand/the provision of 'faflsection of waveguide .adjustable .in -=leng.th

andjperniitting change indirection.

.Due'tothe .rigidity'of the materials used and the typefof construction .thathas been necessary, installations .of waveguides '.for the transmission ofhig'hffrequency" venergy.havefl loeen confined to those 6f apermanent .or.semi-,permanent nature. This has greatly restricted their use because in any types ofainstallations where waveguides would have been of great advantage over cables oizsome other .typeiof flexible transmission line the use .of'the.latter haslbeen dietatedby the 'requirements of retaining .fiexibility .and adjustability of 'lengthaiter' the installation .has been completed.

scams. (0!. 178- 44) It is an object offthis invention to devise a section of waveguide that is 'fiexibleand adjustable.

A further obj ect ofthe .inventionkis to -.devise a "flexible and adjustable .section of waveguide which will not introduce anyelectrical discontinuity that'wouldcause excessive reflection orexcess'ive standingfw'ave ratios.

Generally a device.made.in-ac-cordancewith the 1 same embodiment of the .invention connected to;

a rigidwaveguide system; and

Part) is of rectangular shape and-hasinternal crossesectional dimensions slightly smaller than those of: rigid waveguide. section 11 towhich -it is attachedfloyanyv suitable means'such as flanges l2.-and l3 and bolts =14. Theinternal-'cross-seci tionaldimensions-of; part ['0 are-designed so that itscharacteristic impedance will beequal to that ofrigid waveguide section H. In J. .C. .Slaters,

Microwave 'Iransmission,j" publ-ished ;by; .lVic

:Book Company, Inc., 1942; page 185,1

Grew-Hill -22 V the .formula for .the,characteristic..impedance of arectangularwaveguide is-given: as .follows:

1T 1 -b n/ e 2a) where: Ze q-.is=: the equivalent ror characteristic impedance of-a.-rectangu1ar waveguide in the FITEQni) anode u: is the permeabilityof the dielectric aused e is; the dielectric Constant -.of the die1ectricused m :isvthe-wave length in =iree. space corresponding .to the operating .-freq.uency bzisthe smallerinternal dimension a .is *the 'largerinternaldimension In the design off-the instant waveguide itis desired that the characteristic impedance of the part [0 be equal to that ofrigidwaveguidesection I l 3 *If -a-and bare the respective larger and smaller "dimensions of the part i I 0, l and if we"call A and B the respe'ctive larger and-smaller dimensionsof the rigid waveguide section H, then' by equating we obtain:

,Similar. formulas .may be i used .for other modes of. operation and other-types of waveguides.

'{The .length-.of .,part 4.0; is. equal .to one-half the Waveguide wavelength corresponding :to the toperating ,irequenoy. .The. end of pa-rt .-I 0 has-two two.hol es .L5, 15 vto-connectspart lfl .to.pai;t- 4.6 as

explained hereinbelow.

.Rart l-iimay be of any desired length-1 but rpreierahlyw is longerathan part .mtand has intern-a1 crossesectional -.dimensions'- theasameas .those of rigid waveguideasectiona-l I. --It iS .connected .at one end .to -a .rigid waveguide section .4 1 by flanges IB-and I. 9-.and 'bo1ts-20,-.-similar'to those connecting :part 1 I] to rigid waveguide section-l l,

or by any other suitable method. The sides of part l6 where the current" flow is longitudinal, .the

top ,andibottom -as shown :in the draw-ings,,- are provided with centrally located longitudinal slots 2 I ,1! Slots.2 l, Z I -areadapted to receiveiadjust able clamping devices comprising .bolts .223 22, 'conta.ct..spacer 23,,springs 24, =24,-.and win .nuts' it is obvious that the relative positions of parts I and I6 may be adjusted and then fixed by tightening nuts 25, 25 on bolts 22, 22 in slots 21, 2|. Contact spacer 23 consists of a rectangular conductive member having inner cross-sectional dimensions so that it fits tightly over the end of part I!) and has outer cross-sectional dimensions a little smaller than the corresponding internal cross-sectional dimensions of part I6.

From the above description of a device embodying this invention it is obvious that a flexible and extendable section of waveguide has been provided.

The length of the section is determined by the 2 amount of telescoping of part l0 into part l6 which is adjusted by the position of bolts 22, 22 in slots 2|, 2 l. Angular displacement in both vertical and horizontal directions is made possible by the fact that the outer dimensions of contact spacer 23 is smaller than the internal dimensions of part [6 thus providing clearance on all sides and by the fact that part [6 is appreciably smaller than part I 6 thus allowing large clearance where part It) enters part I6.

It will now be shown how a section embodying the principles of this invention reduces electrical discontinuity to a minimum. Consideringthe energy to be passing-from left to right, it encounters a discontinuity at the shoulder 26 formed by flange l2 since the dimensions of the path of the field are appreciably reduced at that point. This discontinuity arises solely from this physical change and not from any change in characteristic impedance because, as above stated, part I0 is so designed that it has the same character--' istic impedance as that of rigid waveguide section II. Therefore, reflections arising at this point are kept at a minimum.

As the energy continues, the next place 1 at l6 because at this point there is again a change in dimensions. However, the change in dimensions here is of the same magnitude as that at shoulder 26 and in the opposite direction, that is, from small to large. The resultant reflections, therefore, are of substantially equal magnitude. Since part In is one-half of a waveguide wavelength long, shoulders 26 and 21 at which these two discontinuities occur are separated by onehalf the wavelength of the operating frequency and any reflections arising therefrom will ofiset each other. The result is that, although there will be standing waves along part In, these will not be transmitted along the waveguide in either direction. Since the characteristic impedances of parts in and I6 are the same, there is no discontinuity arising due to any change of impedance.

In analyzing the operation of this telescoping section it is convenient to consider the dlscon tinuities presented at shoulder 26 and at shoulder 21 as lumped impedances at those points having substantially the same magnitude which are conjugates of each other and which are separated causes a minimum interference in current flow 7 bottom walls of part l6 where the longitudinal flow of current is of highest value. Contact at the side walls of part I6 is not necessary because the current flow on those walls is transverse, that is, up and down these sides, and no current passes along those walls from one telescoping part to the other.

It has been explained that the internal crosssectional dimensions of part l0 are made somewhat smaller than the corresponding dimensions of rigid waveguide section I I. These dimensions,

however, should not be made so much smaller that energy is unable to pass through part l0 in the same mode in which it is transmitted through rigid section ll. An additional reason for not making these dimensions a great deal smaller than those of rigid section I1 is that the larger the change in dimensions the greater the reflections at shoulders 26 and 21. These dimensions should be made as close to those of rigid waveguide section as fitting of the parts and operation of the device will allow.

It is thus seen that a device employing the principles of the present invention presents a flexible and adjustable waveguide section all elements of which have the same characteristic impedance, the points of electrical discontinuity of which are spaced so that reflections offset each other, and a minimum of interruption of current flow is caused by adjustment and setting means.

Several of these adjustable sections may be used together to achieve a considerable cumulative change in the physical direction of the waveguide or in the amount of adjustment of length.

The embodiment herein described and explained is based onthe usualmode of operation of a rectangular waveguide, but it is to be understood that the principles of this invention apply with equal efi'ectto and result in similar advantages for other modes of operation and apply to waveguides ofvarious shapes and types.

While there has been here described what is at present considered to be the preferred embodiment of this invention it will be obvious to those skilled in the art that various changes and modiin which b is the smaller of the two internal dimensions of said second part, a is the larger internal dimension of that part, B and A are the corresponding internal dimensions of the part having the same internal dimensions as the WES/'3'.

guide system and x is the wavelength in free space corresponding to the operating frequency,

said second part having a length of one-half.

waveguide wavelength of the operating frequency.

2. l he device according to claim 1, which further includes longitudinal slots formed in said first part in those walls thereof wherein current flow is in a direction that is parallel to the longest axis of said part and clamping means extending through said second part and said slots whereby said wave guide parts may be fixed relative to each other.

3. The device according to claim 1, and contact spacer means positioned about that end of said second part that is telescoped into said first part, said contact spacer means having smaller external dimensions than the internal dimensions of said first part whereby said parts may be angularly adjusted.

4. The device according to claim 3, and clamping means extending through said second part, said contact spacer means and said first part whereby said wave guide parts may be fixed relative to each other.

5. The device according to claim 1, which further includes longitudinal slots formed in said first part in those walls thereof wherein current flow is in a direction that is parallel to the longest axis of said part, contact spacer means positioned about that end of said second part that is telescoped into said first part, said contact spacer REFERENCES CITED The following references are of record in the V file of this patent:

UNITED STATES PATENTS Number Name Date 1,921,117 Darbord Aug. 8, 1933 2,106,769 Southworth Feb. 1, 1938 2,165,961 Cork July 11, 1939 2,233,166 Hahn Feb. 25, 1941 2,267,371 Buschbeck Dec. 23, 1941 2,408,745 Espley Oct. 8, 1946 2,427,094 Evans Sept. 9, 1947 

